1. Field of the Invention
The present invention relates to a method for manufacturing a can body such as a bottle-shaped can or an aerosol can, which has a cylindrical trunk portion necked gradually at its upper portion to form a sloped shoulder portion. More particularly, the invention relates to a can body manufacturing method capable of printing a pattern or letter without any distortion not only on the can trunk portion having a completely shaped shoulder portion but also on the shoulder portion.
Here, the word “sloped”, as used herein, also means a curved face whose longitudinal section is arcuate, such as a domed shape.
Moreover, the can, as called herein the “bottle-shaped can”, also means the can, which is provided with a sloped shoulder portion having the diameter getting smaller from the trunk portion to the leading end, and a cylindrical neck portion merging into said shoulder portion, and covers both cans having and not having a thread portion in its neck portion.
2. Discussion of the Related Art
In recent years, Japan has used a number of such bottle-shaped aluminum cans in the market of beverage cans that a cylindrical and thin trunk portion and a diametrically-small threaded neck portion are integrally shaped through a smoothly sloped shoulder portion. This is because the bottle-shaped can of this kind can be sealed (and resealed) with a threaded cap, and because it is excellent in the container recycling (or raw material reusing) percentage, the shading properties, the gas permeability and the quick content cooling properties. The bottle-shaped cans made of aluminum have been recently employed for beverages also in the United States of America.
Two kinds of resealable bottle-shaped cans have generally spread in the Japanese market. One is the bottle-shaped can of the type, in which a threaded neck portion of a diametrically-small cylindrical shape, a domed shoulder portion and a diametrically-large cylindrical trunk portion are shaped integrally, and in which a separate bottom lid is seamed and fixed on the lower end opening side of the trunk portion. The other is the bottle-shaped can of the type, in which a threaded neck portion of a diametrically-small cylindrical shape, a shoulder portion, a diametrically-large cylindrical trunk portion and a bottom portion are shaped integrally, and in which a frusto-conical or domed shape shoulder portion is formed between the trunk portion and the neck portion.
The neck portion of the bottle-shaped can of the latter type is diametrically larger by about 10 mm than that of the bottle-shaped can of the former type. In the bottle-shaped can of either type, the opening portion can be resealed by putting a Pilfer proof cap on that neck portion.
The method for shaping the bottle-shaped can of the former type is disclosed, for example, in U.S. Pat. Nos. 6,857,304, 6,499,329 and 5,718,352. The method for shaping the bottle-shaped can of the latter type is disclosed in detail, for example, in U.S. Pat. Nos. 5,718,352, 5,704,240 and 6,779,677. Moreover, the method for shaping a shoulder portion having a smooth sloped face, by shaping a bottomed long cup in which one of the end portion is opened from an aluminum sheet or an aluminum sheet alloy, and then necking the open side more than once to reduce the diameter gradually, is disclosed in U.S. Pat. Nos. 5,293,765 and 5,355,710.
To the outer face of such bottle-shaped can, there is applied a printed decoration (i.e., a decorative design made by a print) such as a pattern or letters. One example of this method is described on the bottle-shaped can of the former type. In the prior art, a can body is shaped at first and is then printed. Specifically, a lubricant is applied to both faces of a metal sheet material such as an aluminum alloy sheet having or not a thermoplastic resin coating layer on its both faces. Then, the metal sheet material is subjected to a punching and a drawing to form a shallow cup. Next, this shallow cup is subjected to a re-drawing to reduce the diameter of the cup and to increase the height of the cup, and subjected further to a thinning treatment such as a stretching or an ironing to thin the trunk wall of the cup. Consequently, a bottomed cylindrical long cup having a large height (i.e., a one-end opened seamless can) is shaped. The drawing is applied to the bottom side of this long cup more than once, so as to shape a diametrically-small bottomed cylindrical portion (or a neck portion) and a shoulder portion sloped in a dome shape or a frusto-conical shape. After this, the lubricant is removed from at least the outer face of the long cup, and the outer face of the cylindrical trunk portion is printed. Besides, a printed film may be adhered to the outer face of the can instead of this printing.
This shaping method is disclosed in detail in the specification of U.S. Pat. No. 6,463,776 and is expected to understand itself well by reference. Therefore, a further explanation is omitted.
Here, it is widely executed in the field of can manufacturers to print the outer face of such long cup or can. The printing speed of the long cup is usually about 1,000 cans/minutes or higher.
The long cup having the print on the outer face of its trunk portion is opened by cutting off the leading end portion of the diametrically-small bottomed cylindrical portion (or the neck portion). This opened leading end portion of the diametrically-small cylindrical portion is subjected to a curling to form a curled portion and is subjected to a threading to form a thread on the cylindrical portion below the curled portion. The cylindrical portion below the treated portion is rolled to form an annular recess.
Here, the curling is not necessarily to be carried out prior to the threading, but may be carried out after the threading. It is also possible to start the curling at first and interrupt it midway to carry out the threading, and then complete the remaining curling.
Subsequently, the opening end portion of the diametrically-large cylindrical trunk portion on the opposite side of the neck portion is subjected to a necking-in to reduce the diameter of the opening end portion, and then subjected to a flanging treatment to bend its leading end outward. After this, the opening end portion is seamed with a separate bottom lid. This shaping process is disclosed in U.S. Pat. No. 6,499,329.
According to the method thus far described, however, the long cup is shaped to have the shoulder portion and the bottomed diametrically-small cylindrical portion (i.e., the unopened neck portion), and then a printed decoration such as a pattern or letters is applied to the outer face of the cylindrical trunk portion. Therefore, the printed decoration is not applied in the least to the shoulder portion, which occupies a relatively large area of the bottle-shaped can.
This is reasoned in the following. There exists a printer for printing such sloped portion. However, a printing speed of this printer is a rather slow. Therefore, it is substantially impossible to print the sloped shoulder portion of the bottle-shaped can at a speed of 100 cans/minutes or higher.
In the specification of U.S. Pat. No. 6,463,776, on the other hand, there is disclosed a method for applying a printed decoration to the sloped shoulder portion. This method will be described briefly. The lubricant is removed from at least the outer face of the long cup before the diametrically-small bottomed cylindrical portion and the sloped (or domed or frusto-conical) shoulder portion are formed. Then, the outer face of the trunk portion of the long cup is printed with a pattern or letters, a clear coating film for protecting the printed layer is applied on the printed layer, and the printed layer and the coating film are dried. After this, a lubricant is applied again to at least the outer face of the long cup. Then, the bottom side of the long cup is subjected to a drawing more than once and to a reforming once, so as to form a diametrically-small bottomed cylindrical portion and a smoothly sloped shoulder portion. By way of these steps, the printed decoration is applied not only to the trunk portion of the bottle-shaped can but also to the sloped shoulder portion.
On the other hand, one example of the method for manufacturing the bottle-shaped can of the latter type having a neck portion of a relatively large diameter is disclosed in U.S. Pat. No. 5,293,765. According to this method, a long cup is formed at first. Specifically, a metal sheet material (or an aluminum alloy sheet), which is prepared by applying a lubricant to the both faces of a highly pure, relatively thick aluminum sheet, is subjected to an impacting to shape a bottomed cylindrical long cup all at once. Alternatively, this bottomed cylindrical long cup is shaped by forming a shallow cup by applying a punching and a drawing to a relatively thin aluminum alloy sheet in which a lubricant is applied to both faces, and then applying a re-drawing and an ironing to the shallow cup. The long cup thus formed is trimmed on its opening side to make the longitudinal length even, and then, a lubricant removing treatment, and a degreasing/chemical conversion/rinsing treatments for improving adhesiveness of the printing ink and the paint with the inner and outer surfaces of the cup, is applied to both inner and outer faces of the cup. After this, a decorative print and a clear coating (e.g., finishing varnish) for protecting the printed face are applied at least the outer circumference of the trunk portion of the cup. Moreover, the cup is sprayed on its entire inner face with a protecting paint.
After this, the trunk portion of the long cup is subjected to a mouth drawing or a multiple necking-in repeatedly more than one time, thereby to form the diametrically-small cylindrical neck portion and the frusto-conical shoulder portion. Then, a threaded portion is formed in the central portion of the neck portion.
If desired, a curled portion may be formed on the leading end of the neck portion, and an annular recess may also be formed below the threaded portion (as referred to JP-A-2000-191006).
As disclosed in the specifications of U.S. Pat. Nos. 4,098,420 and 4,256,233, for example, there is known an easily openable aluminum cap with a tab, comprising: a top portion; a skirt portion depending from the circumferential edge of the top portion; the tab extending from the skirt portion to be pinched by fingers; a seal member on the inner face side near the boundary between the top portion and the skirt portion; and a score line (or a notch line) extending from the skirt portion near the two sides of the tab to the top portion. This aluminum cap is put on the neck portion of the bottle-shaped can, and the lower portion of the skirt portion of the cap is crimped (or bent inward) by a capper to seal the neck portion of the bottle-shaped can. In case this cap is used, therefore, the cap is put on the neck portion by a crimping. This makes it unnecessary to form the threaded portion in the neck portion of the bottle-shaped can, but makes it sufficient to form the curled portion at the upper end of the neck portion.
In the case of the aerosol can, on the other hand, the shoulder portion can be formed by a shaping method similar to that of the case of the bottle-shaped can, i.e., by the drawing, the reforming and the necking-in.
One example of this shaping procedure is briefly described. First of all, the steps to that of forming the long cup are absolutely identical to those of the bottle-shaped can manufacturing process so that their description is omitted. Next, the lubricant is removed from at least the outer face side of the long cup, and the open end of the long cup is trimmed to have an even height. Then, the outer face side of the trunk portion of the long cup is printed substantially all over its surface with a pattern or letters, and the protective clear coating is instantly applied to the printed face. After this, the printing ink layer and the coating layer are dried.
Although the printing step and the coating step of the long cup is not limited to the above method, it may also be carried out by the dry offset printing method, which uses the dry offset printing/coating apparatus for a two-piece can, and which is well known and commonly used in the can manufacturing field.
Here, the material for shaping the long cup may be exemplified not only by the resin-coated metal sheet, which is provided in advance on both faces of a metal sheet with a protective coating film such as a thermoplastic resin coating layer or a thermosetting resin coating layer, but also by a metal sheet which is not coated with any resin.
In case the metal sheet having no resin coating is used, for example, the long cup is shaped by a shaping process similar to the aforementioned one after the lubricant was applied to both faces of the metal sheet.
Next, the long cup is trimmed at its open end side to have an even height and is cleared of the shaping lubricant sticking to the inner and outer faces thereof. Moreover, the long cup is subjected on its two faces to a surface treatment such as a forming treatment and is dried. After this, an outer face of the trunk portion of the long cup is printed and protectively coated, and an outer face of the bottom portion and its vicinity is protectively coated. On the other hand, an inner face of the long cup is also protectively coated. In other words, the timing of the trimming step of the open end side, and an application of the protection coating to the outer face of the bottom portion of the long cup and its vicinity and to the inner face of the long cup, are different from that of the case, in which the long cup is shaped from the resin-coated metal sheet, which is provided in advance on its two faces with the resin film.
After this, the lubricant is applied to at least the outer face (i.e., the outer faces of the trunk portion and the bottom portion) of the long cup. Then, the long cup is subjected at its bottom portion to plural drawings as for the aforementioned bottle-shaped can, and is subjected to the reforming to form the shoulder portion having a dome shape (or a frusto-conical shape) and the bottomed diametrically-small cylindrical portion. The shoulder portion thus shaped is printed on at least one half of the trunk portion.
After this, the leading end portion of the diametrically-small cylindrical portion is cut and opened, and the open end portion thus formed is curled outwardly to form the curled portion. Moreover, the trunk portion is subjected at its open end portion to the necking-in and the flanging, and the flanged portion is fixedly seamed with a separate bottom lid thereby to complete the aerosol can.
On the other hand, the method for manufacturing the aerosol can of the type, in which the open end of the long cup is repeatedly subjected to plural necking-in treatments so that it is diametrically reduced to form the sloped shoulder portion and the diametrically-small cylindrical neck portion, is exemplified by the following manufacturing process. The illustration of this manufacturing process is omitted.
The metal sheet, which is prepared by coating its two faces with the thermoplastic resin film and by coating the two faces with a high-temperature volatile lubricant, is subjected to the punching to produce a blank. This blank is subjected to a drawing to form a shallow cup. This shallow cup is subjected to plural drawings and plural ironings to form a flanged long cup. After this, this long cup is heated to volatilize and remove the lubricant from its outer face, and is trimmed at its open end to an even height.
After this, the trunk portion of the long cup is printed and coated all over its face by the dry offset printing method, and the printed ink layer and the coating layer are dried.
After this, the lubricant is applied to the open end side of the outer face of the trunk portion of the long cup. Then, the open end portion of the long cup is repeatedly subjected to drawings of multiple times or to necking-in treatments of multiple stages thereby to form the frusto-conical or domed shoulder portion and the diametrically-small cylindrical short neck portion.
After this, the leading end portion of the neck portion is trimmed and then curled outwardly to form the curled portion. As a result, there is completed the bottomed long aerosol can, in which not only the trunk portion but also the shoulder portion are printed, and in which the bottom portion, the trunk portion and the shoulder portion are integrally formed.
No matter what type of the can, e.g., the aforementioned bottle-shaped can or the aerosol can, the printed decoration is applied to the cylindrical trunk portion of the long cup before the smooth shoulder portion (and the neck portion) is formed. Thus, the printed decoration is applied not only to the formed trunk portion of the can body but also to the sloped shoulder portion.
However, the following problems arise in the can thus shaped in that sequence.
This is described on the example of the case, in which the bottom portion of the long cup is subjected to plural drawings.
Specifically, if the printed decoration to be applied to the portion near the bottom of the cylindrical trunk portion of the long cup (i.e., the portion to be formed into the shoulder portion by the subsequent treatment) is a pattern or letters having a clear shape, the pattern or letters applied to said portion are deformed and distorted by the subsequent treatment. Specifically, the applied pattern or letters are converged and get thinner (or narrower) in upward direction (i.e., to the bottom portion), according to the progress of the reshaping (or the reforming) of said portion from the cylindrical shape to the sloped shoulder portion.
Especially, in case the pattern or letters is applied over the trunk portion and the shoulder portion of the can body, only a portion i.e., the shoulder portion is tapered. This gives such an impression that the applied pattern or letters is/are considerably distorted in its entirety.
This example is shown in FIG. 7A and FIG. 7B. The lefthand drawings present a printed decoration 52 printed on a trunk portion outer face 51 of a long cup 50, and the righthand drawings present a printed decoration 56 of a bottle-shaped can 55 just after a diametrically-small neck portion 53 and a domed shoulder portion 54 were formed.
This likewise occurs in case the aerosol can, the shoulder portion of which is formed by a similar method.
On the other hand, in case of the bottle-shaped can (or the aerosol can), which is prepared by subjecting the open end side of a long cup printed all over its cylindrical trunk portion with the printed decoration to the drawings of multiple times and the necking-in treatments of multiple stages thereby to form a smoothly sloped shoulder portion and a diametrically-small cylindrical portion (or a smoothly sloped shoulder portion), the bottle-shaped can is troubled by a problem that the printed decoration applied to the sloped shoulder portion below the open end is converged.